Typically, transistors of a semiconductor chip used in an electronic device are connected to one another through a pattern of interconnect trenches formed within a dielectric layer. The pattern arrangements usually have a damascene or dual damascene structure. A barrier layer covers the patterned dielectric layer and a metal layer covers the barrier layer. The metal layer has at least sufficient thickness to fill the patterned trenches with metal to form circuit interconnects.
Interconnect trenches must have sufficiently high density and degree of complexity to manufacture a device comprising transistors whose intervals are 0.25 μm or less. Thus, chemical mechanical polishing (CMP) is required for effective and efficient use of the transistors. Typical metal interconnect CMP necessitates multiple polishing steps. For example, the first step is carried out to essentially remove excess metal interconnects, such as copper interconnects, at an initial high rate (>5,000 Å/min.), and then the second step is carried out to remove a portion of the metal that remains on a barrier layer outside of the metal interconnects and maximize the surface planarity of the metal interconnects using a finely divided abrasive. Subsequent polishing removes the barrier from an underlying dielectric layer to provide a planar polished surface on the metal interconnects embedded in a damascene or dual damascene structure and the dielectric layer.
The metal within the trenches functions as a metal line forming an interconnect circuit. Metal CMP tends to remove not only metal present outside of a pattern of trenches filled with an interconnect metal but also the interconnect metal present within the trenches. The removal of the metal from the trenches causes a so-called “dishing” phenomenon. Dishing is an unfavorable phenomenon because it causes variations in the critical dimensions of the metal circuit. Serious dishing can generally occur when the metal removal rate is high. Treatment of the metal with a polishing slurry that exhibits a non-Prestonian behavior is considered a method for minimizing dishing and attaining a high degree of planarization.
Earlier copper CMP slurries exhibit linear Prestonian behavior (F. W. Preston. J. Soc. Glass Tech. 11, 214 (1927)). For example, the removal rate of copper is a first-order function of pressure applied to a substrate and polishing rate. This example is indicated by line ♦ in the graph of FIG. 1 (Chen et al. Thin Solid Films 498, 50-55, 2006). Some literature and patent publications disclose that when copper polishing slurries exhibit a non-Prestonian behavior indicated by line ▪ or ▴ in FIG. 1 during copper CMP, high planarization efficiency and low pattern dependency can be accomplished ((a) U.S. Pat. Pub. No. 2006/0000151; (b) U.S. Pat. No. 6,454,819 (2002) to H. Yano, G. et al.; (c) U.S. Pat. No. 6,565,767 (2003) to M. Hattor et al, (d) U.S. Pat. No. 6,821,897 (2004) to D. J. Schroeder et al.; (e) S. Kondo et al. J. Electrochem Soc. 147, 3907 (2000)). That is, the non-Prestonian behavior is observed when the removal rate of copper shows a linear correlation with respect to pressure or polishing rate. Regions with a high topography in a wafer are exposed to relatively high local pressures and are thus removed at high rates. However, the CMP systems (e.g., slurries) exhibiting a non-Prestonian behavior shown in FIG. 1 polish high-topography regions at much lower rates than slurries exhibiting a Prestonian behavior. In conclusion, slurries exhibiting a non-Prestonian behavior can widen over-polishing window of copper CMP to planarize copper in a more efficient and rapid manner.
Non-Prestonian behavior can be induced by using copper CMP slurries utilizing the following polymers:
Homopolymers: polyacrylic acid and polymethacrylic acid (U.S. Pat. No. 6,117,775);
Heteropolymers: polyacrylate-polymethacrylate copolymers (U.S. Pat. No. 6,632,259, U.S. Pat. Pub. Nos. 2006/0000150 and 2006/0000151);
Polymer mixtures: polyacrylic acid and polyvinylpyrrolidone (U.S. Pat. Pub. Nos. 2007/0176141 and 2006/0138086), polyacrylic acid and polysulfonic acid (U.S. Pat. Pub. No. 2006/0191872);
Blends with polymers: zwitterions and polyacrylic acid (U.S. Pat. Pub. Nos. 2005/0189322 and 2007/0007248), quaternary ammonium ions and polyacrylic acid (U.S. Pat. Pub. No. 2006/0205219), benzotriazole (BTA) and homopolymers (U.S. Pat. Nos. 6,899,821 and 6,896,825 and U.S. Pat. Pub. No. 2005/0095860), BTA and polyacrylic acid (U.S. Pat. No. 6,461,230).
However, the conventional polishing systems are not satisfactory in effectively exhibiting a non-Prestonian behavior.